Currently, many digital cameras have a zoom lens, and a single image sensor for capturing still and motion images. The captured images are then digitally processed to produce digital image files, which are stored in a digital memory in the camera. The digital image files can then be transferred to a computer and displayed, or transferred to a printer and printed.
Small camera size and large optical zoom range are very important features of digital cameras. Users prefer to have a large zoom range rather than a limited zoom range. Unfortunately, providing a large zoom range lens, without sacrificing the quality of the captured images, increases the size of the digital camera. With higher cost cameras, such as single-lens reflex cameras, these problems are sometimes addressed by using multiple, interchangeable zoom lenses, such as a 28-70 mm zoom and a 70-210 mm zoom. Such an option, however, is inconvenient for a user of a compact digital camera.
Some digital cameras use a single lens and multiple image sensors to form a color image. Light from a target is separated into multiple colors by a prism beam splitter, and multiple monochrome image sensors are used to capture red, green, and blue color images.
Stereo film cameras and stereo digital cameras are known in the related art. These cameras have two horizontally-separated lenses of the same focal length, which form slightly different images of the scene onto two frames of film or two image sensors. The two images provide a so-called “stereo pair.” The two lenses are designed to provide the same magnification, and both are used to simultaneously capture left-eye and right-eye images on a pair of image sensors in order to achieve a stereo effect.
In a compact digital camera, in order to obtain a large zoom range without incurring the cost of lens exchange, the digital camera is preferably equipped with multiple lenses having different focal lengths, and the multiple lenses are used distinctively according to a zoom position. When, for example, two lenses having different focal lengths are equipped on a camera, how the focal lengths are set is important, as is how the two lenses are switched, because a digital camera offers an electronic zoom function for electronically zooming digital image data in addition to the optical zoom function.
Japanese Patent Laid-Open Publication No. Hei 10-42183 discloses a camera having one lens and one image sensor in which an angle of view is determined by driving an electronic zoom and an optical zoom, and a percentage of the optical zoom is increased while the angle of view is maintained.
Japanese Patent Laid-Open Publication No. 2003-283910 discloses a camera having an optical finder and a zoom finder wherein the finders are suitably switched and, when the finder is switched from the electronic finder to the optical finder, the lens of the optical finder system is driven in connection with an image-capturing lens so that the angles of view match.
The above-described related art references relate to a camera having one lens and one image sensor and do not relate to a camera system having multiple optical systems for capturing images of a scene. Thus, none of these references disclose how the optical system is switched among the multiple optical systems.
Consider a digital camera having two lenses including a fixed focal length lens and a zoom lens. Switching of these two lenses is performed as follows. A focal length gap between the focal length of the fixed focal length lens and a minimum focal length of the zoom lens is interpolated by an electronic zoom of a digital image obtained by the fixed focal length lens. The camera is provided with a zoom-setting unit (zoom button) for setting a zoom position, and the user can set the zoom setting unit to the wide side (wider angle) or to the tele side (narrower angle) so that the user can capture images at a desired zoom position. When the user sets the zoom-setting unit provided on the camera to “tele,” the digital image obtained by the fixed focal length lens is electronically zoomed in, the lens is switched to the zoom lens when a tele end of the electric zoom is reached, and the optical zoom is performed using the zoom lens. When, on the other hand, the user operates the zoom setting unit to set the zoom setting unit to “wide,” a digital image is obtained by optical zoom-out, the lens is switched to the electronic zoom of the fixed focal length lens when the minimum focal length of the zoom lens is reached, and the camera is zoomed out using the fixed focal length lens.
FIG. 15 schematically shows an electronic zoom range and an optical zoom range of a digital camera having a fixed focal length lens corresponding to 20 mm in a 35-mm film camera and a zoom lens corresponding to 40 mm-120 mm in a 35-mm film camera. In this structure, there is a focal length gap in 20 mm-40 mm between the 20 mm fixed focal length lens and the 40 mm-120 mm zoom lens. An electronic zoom range 700 of the 20 mm fixed focal length lens is set so as to fill in the focal length gap. The focal length of the wide end (an end near the wide angle) of the electronic zoom range 700 of the 20 mm fixed focal length lens is represented as IDW (20 mm) and a focal length of the tele end (an end near the tele side) is represented as IDT (40 mm). A focal length of the wide end of an optical zoom range 800 of the zoom lens is represented as IIOW (40 mm) and a focal length at the tele end is represented as IIOT (120 mm). In general, because the electronic zoom zooms in by interpolating the original digital image, the electronic zoom causes degradation in image quality. Therefore, as is easily seen, the lens should be switched to the zoom lens within the optical zoom range of the zoom lens. Therefore, when the user operates the zoom setting unit towards “tele,” the lens is switched from the fixed focal length lens to the zoom lens to transition to the optical zoom range 800 when the tele end IDT of the electronic zoom range 700 is reached. When, on the other hand, the user operates the zoom setting unit to “wide,” the lens is switched from the zoom lens to the fixed focal length lens to transition to the electrical zoom range 700 when the wide end IIOW of the optical zoom range 800 is reached.
FIG. 16 shows zoom ranges in a case (A) in which the user sets the zoom setting unit to “wide” so that the captured image is transitioned from tele to wide and those in a case (B) in which the user sets the zoom setting unit to “tele” to transition the captured image from wide to tele. In FIG. 16(A), in the electronic zoom range 700, electronic zoom-out of the digital image obtained by the fixed focal length lens is performed according to the “wide” operation of the zoom setting unit by the user. In the optical zoom range 800, on the other hand, optical zoom-out of the digital image obtained by the zoom lens is performed. When the zoom position of the zoom lens reaches the minimum focal length IIOW of the zoom lens; that is, the wide end of the optical zoom range 800 during execution of the optical zoom-out process, the optical system capturing an image of the scene is switched from the zoom lens to the fixed focal length lens. In FIG. 16(B), in the electronic zoom range 700, an electronic zoom-in process of the digital image obtained by the fixed focal length lens is performed. In the optical zoom range 800, an optical zoom-in process of the digital image obtained by the zoom lens is performed. When the tele end IDT of the electronic zoom range is reached during execution of the electronic zoom-in process, the optical system capturing an image of the scene is switched from the fixed focal length lens to the zoom lens.
In the above-described structure in which a tele end of the electronic zoom of the fixed focal length lens and the wide end of the optical zoom of the zoom lens are matched and the lens is switched at this focal length, there arises a problem in that switching of the lenses frequently occurs around the focal length of 40 mm; for example, around a position 900 in FIG. 16. The zoomed image in which the digital image obtained by the fixed focal length lens is electronically zoomed and the zoomed image in which the digital image is optically zoomed by the zoom lens differ in image quality even when the angle of view is identical. Therefore, when switching of lenses occurs frequently, the user would see switching between images having different image qualities even though the angle of view is identical, which is inconvenient.